Transformer



Dec. 14 1926.

J. S. LENNOX TRANSFORMER Filed Sept. 18. 1923 m w w m John Jf Lennox,

. H/SA ttorn ey.

Patented Dec. 14, 1926.

UNITED. sr ras PATENT OFFICE.

JOHN s. LENNOX, or

rrr'rsrmnn, MASSACHUSETTS, assrenon r ennnnarf ELECTRIC oomranr, A CORPORATION or EW YORK.

TRANSFQRMER.

Application filed September My invention relates to transformers; In the operation of a transformer,- the main magnetieflux which links both'the primary an secondary windings is substantially confined to the-magnetic core, but there is always some-leakage orstray, flux which leaves the windin s and then finds its way back: into eddy current losses. These-losses notohly them t rough pathsoutside the core. In some transformers, the amount of] leakage flux is; considerable, "especially in transformers having .large reactance, and it always seeks the easiest return pathswhich may include winding and core clampsfiand other structural magnetic parts which are not I formed of proper material norsuitablydami nated to prevent objactionable*hystereslsand reduce the efliciency I of the transformer but appear in the form of heat which may raise the temperature at the -points where the losses occur to such an extent as to cause.

injury to adjacent insulation used .in the transformer structure: In'the case of .an oil immersed transformer, the heat resulting from stray magnetic fliix mayv cause-deteri'- resistance between the laminationsjservin'g toreduce eddy currents which would otherwise cause objectionable losses andheating.

However, if the magnetic' flux is permitted to enter or leave'the core inadirection across the laminations,: it will produce eddy cur rents and consequent losses and heating con- 18 3:923. Serial No. 663,469.

which Fig. 1 is a View in elevation of a core 1 type transformer provided with auxiliary lamina-ted stray-flux paths in accordance with'the invention, Fig. 2 is a plan view of v the transformer shown in Fig. 1, Fig. 3 is a detail view showing a modification, Fig. 4 1s a view in elevation of a three phase transformer provided with laminated stray flux paths in accordance with the invention, Fig. 5 is an end view of the transformer shown Fig. 1 in connection with a single phase core in Fig. 4, Fig.6 is a plan view, partly broken One form of the invention is shown in type transformer. The transformer includes a core lhaving two winding legs, each winding legfbeing surrounded by a stack of interleaved high tension winding coils 2 and low tension winding coils 8. By reason of the low-reluctance of the core as compared with that of the air or otherdielectric surrounding the windings most of the magnetic flux v produced hycurrent in the primary coils-is confined to the core. There is, however, an appreciable. and often a considerable amount of so-called stray or leakage flux which is produced by the primary winding and which follows paths whlch are entirely or partially outside the core. The leakage flux from transformer'windings of the interleaved type such as those shownin Figs. 1 and 2 leave the windings from the spaces between the primary and secondary'winding sections or coils and'reenter the windings through other similar spaces. This is true, of course, both insideand outside of each coil stack. The primary; winding may be either the low tensiderably greater than if itenters or'leaves- :sion or the high tensionwinding, depending the core edgewise. of the laminations so that noneof the flllX passes perpendicularly through any of thelaminations. Another object of the inventionis to reduce losses and heating by providing auxiliary laminated aths for reducin the amount of stray or l eakage flux whicli entersor leaves the core lam'inations otherwise than edgew'ise thereof.

Qther objects and advantages will appear upon whether the transformer is to step the voltage upor down. The stra flux inside .each stack of windings willo course pass through the laminated winding le .of the core as this is thepathlof least re uctance. The' effect of that portion of the stray flux which enters and leaves the core 1e cdgewise of the laminations is-not apprecia 1y objec tionable'as the reluctance between lamina tions confines each element of fiux'to a single lamination and so prevents appreciable eddy currents in the core. It-anyof this flux, however, is permitted to enter or leave the core leg crosswise of the laminations, it will produce eddy currents with consequent losses and heating. In accordance with the invention, therefore, auxiliary laminated magnetic members 4 are mounted on the faces of the outside core laminations to divert'stray flux from paths transversely intercepting the laminations and thus to shield the core leg from flux approaching 1t crosswise of its laminations. The laminations of these auxiliary shielding members 4 are at right angles to the laminations of the shieldedcore leg so that the stray flux will enterand leave them edgewise with minimum resulting eddy currents.

Another form of auxiliary laminated member 5 is indicated in Fig. 3. This form is similar to the auxiliary members 4 of Figs.v

1 and 2 but its laminations are parallel instead of at right angles to those of the core 1.

Theends of the laminations are stepped, the outer lamination being shortest and those beneath it being progressively longer and longer. Stray flux approaching the core nea the end of the laminated member 5 can obviously enter the laminations through their end edges and pass throughthem. withoutreaching the core 1 and without causing objectionable eddy currents. Auxiliary members of this form may be of suitable lengths and locations to 'bring'their stepped .cnds into the paths of the leakage flux between the' windings and core and so prevent this flux from entering the core.

Another form of the invention is shown in Figs. 4, 5-, and 6 in connection with a three phase transformer having concentric cylindrical windings. The core 6 has three winding legs 7, each winding leg being surrounded by the high and low tension cylindrical windings 8 and 9 of one of the three phases. The windings are supported between core clamps 10 secured to the core yokes. The 4 stray flux here passes through the cylindrical space between the two windings 8 and 9, returning from one end of this space to the other end through any. available path or paths. Whichever the direction of the stray flux may be through the cylindrical space be tween the two windings on any one core leg,

it is always in the opposite direction in at least one and part of the time in both of the cylindrical spaces between the windings on the other core legs so that a large part of the stray flux from any one of these winding spaces .returns through one or both of the other winding spaces. Auxiliary laminated magnetic members 11 are located between the core clamps 10 and the ends of the windings 8 and 9 to provide paths of low reluctanoe between the ends of the winding spaces, the clamps 1O being-thus shielded from the stray flux flowing between the ends of these winding spaces. The laminations of the members 11 are arranged edgewise to,

the direction of the flux as it leaves or enters thewihding s aces to reduceeddycnrrent losses and heal ing. The members 11 are insulated from the clamps 10 to prevent shortcircuiting of the laminations. p

A single phase shell type transformer with concentric cylindricalwindings is shown in member 12 is located at each end of the cylindrical space between the two windings and at each side of the core to receive the stray flux as it leaves this space. The ends of these auxiliary members 12 a're curved in against the inner faces of the core yokes so that the stray flux from one end of the cylindrical winding space may follow the adjacent auxiliarymembers 12 to the inner edges of the yoke lamina-tions', thence edgewise into these laminations, then through the outer legs of ,the core and through theother auxiliary members 12'to the other end of the winding space. The laminations oi the auxiliary membersl2 are arranged edgewise to the direction of the flux as it enters them from the winding space and also as it' leaves them to enter the core yoke. The stray flux is thus prevented from reaching structural parts of the transformer, such as core and coil clamps, which cannot be conveniently laminated and arranged to prevent objectionable eddy current losses.

-"hat I claim as new and desire to secure by Letters Patent ofthe United States is:

1. A. transformerstructure including a laminated magnetic core, windings on said core, and'an auxiliary magnetic member for Fig. 7. An auxiliary laminated magnetic diverting leakage'niagneticfiux away from a path transverselv intercepting to the laminations .of said core.

2. A transformer structure including a laminatedmagnetic core, windings on said core, and an auxiliary magnetic member for changing the direction of the path of leakintercepting the laminations' of said core to a path substantially parallel to said laminaage'magnetic flux from a path transversely 

